Social jetlag and DXA-derived adiposity in Korean adults: A nationwide study using the 2024 Korea National Health and Nutrition Examination Survey

Background Social jetlag, the discrepancy between weekday and weekend sleep timing, is a behavioral marker of circadian timing mismatch and has been linked to obesity, mainly through conventional anthropometric measures. We examined its association with dual-energy X-ray absorptiometry (DXA)-derived adiposity using the nationally representative 2024 Korea National Health and Nutrition Examination Survey (KNHANES). Methods This cross-sectional study included adults aged ≥40 years reporting usual weekday and weekend bedtimes and wake times. Social jetlag, the absolute difference between weekday and weekend sleep midpoints, was categorized as <1 h, 1– < 2 h, and ≥2 h, with ≥2 h as the primary exposure. The primary outcome was DXA-derived total body fat percentage; subtotal and trunk fat percentages were key secondary outcomes. Height, weight, and waist circumference were obtained by standardized KNHANES examination. Survey-weighted linear regression was adjusted for age, sex, height, average sleep duration, income, education, smoking, alcohol use, physical activity, hypertension, and diabetes. Results Among 4,483 participants, 267 (6.0%) had social jetlag ≥2 h. In fully adjusted models, this group had higher total body fat percentage (β = 0.81 percentage points; P = 0.025), subtotal fat percentage (β = 0.86; P = 0.025), and trunk fat percentage (β = 1.01; P = 0.036), but not higher BMI or waist circumference. Associations persisted after adjustment for depressive symptoms, but were attenuated and no longer significant after adjustment for a chronotype-related proxy, and were not reproduced when social jetlag was corrected for sleep debt. Sleep duration variability showed no association. Conclusions Social jetlag ≥2 h was associated with modestly higher DXA-derived total and trunk body fat percentage, differences not captured by BMI or waist circumference. Because the associations did not persist in chronotype-adjusted or sleep-corrected analyses, conventional social jetlag may partly reflect compensatory weekend sleep. These findings are hypothesis-generating and need longitudinal confirmation.